CNC Machining Services for Aluminum Steel Windows Doors

• 1
  Key takeaways
• 2
  Aluminum Steel Windows Doors CNC Machining: Which Route Fits
• 3
  Aluminum or Steel: Pick by Load Path, Not by Habit
• 4
  Set Tolerance per Feature, Not per Drawing
• 5
  Finishing Changes Dimensions: Plan It Into the Drawing
• 6
  What a Shop Must Prove Before You Release Volume
• 7
  Step by Step: From RFQ to Shipped Window and Door Parts

Aluminum wins on weight and corrosion when the frame carries glass and wind load. Extruded 6063-T6 gives a clean anodized face; 6061-T6 and 6082 machine better when you need pockets, slots and threaded holes in a solid billet. A 6 m mullion still weighs less than half of the steel version, which changes crane time and anchor design on site.

Steel wins on strength per millimeter of profile depth. Fire-rated assemblies, security doors and historic restoration often cannot go thicker, so 1018, 4140 or 17-4PH carry the load in the same sightline. The trade is corrosion: steel needs plating, powder coating or black oxide, and every cut edge becomes a rust path if it is left bare.

The mix matters too. Many high-end systems use aluminum frames with stainless hardware, and that pair behaves badly in salt air. Dissimilar metals plus road salt equals galvanic pitting at the hinge. Nylon isolators or a plated barrier at the contact face solve it, and they must be in the drawing before machining starts.

• 1
  Thin sightline, high loadGo steel or 7075, then protect the surface.
• 2
  Long spans, coastal siteGo 6063-T6 or 6082 with anodizing.
• 3
  Mixed frame and hardwareSpecify an isolation layer at the joint.

A blanket ±0.005 mm callout on a 3 m extrusion raises cost and buys nothing. Wind load and thermal movement move a mullion far more than 5 μm. The useful split is by function: hinge and lock pockets, roller slots and miter faces drive fit and weather sealing, so hold those at ±0.02 mm to ±0.05 mm. Drainage holes, weep slots and cover screw holes only need ±0.2 mm.

Datum choice decides whether those numbers hold in the jig and on the wall. Machining from the extrusion's own centerline gives a symmetric profile but drifts against the outer face. Machining from the finished outer face matches how the installer sets the frame. Tell the shop which face is the reference before they build the fixture, not after the first article.

Length matters. On our 4,000 mm travel machines a single setup holds the full mullion, so the hole pattern stays true end to end. Split the part across two setups and you add a re-clamp error that no tolerance band can absorb. For long profiles we also check straightness after machining, because relieving the extrusion skin can let the part bow.

• 1
  Fit-critical features±0.02 to ±0.05 mm on pockets and miters.
• 2
  Non-critical features±0.2 mm is enough for drainage and cover holes.
• 3
  One setup beats twoFewer re-clamps means fewer datum errors.

Anodizing is not paint. Type II clear builds roughly 5–15 μm per side; hardcoat can build 25–50 μm per side and grows into tight corners. A Ø8 mm pin hole becomes undersize after hardcoat, and an M6 thread will not accept its screw. Either cut the thread after coating or mask it, and state the coating thickness on the drawing so the machinist can allow for it.

Powder coating hides tool marks and gives color, but it also rounds sharp edges. A 0.5 mm chamfer disappears under a 60–80 μm film, so if the edge is a visible sightline, ask for a defined chamfer and a masked contact face. Bead blasting before anodizing evens out the sheen but can leave a matte finish that shows handling marks on site.

For steel parts, electroless nickel holds a tighter thickness than zinc plating and keeps the pocket dimensions stable. Black oxide adds almost nothing dimensionally and suits internal hardware that never sees weather. Whatever the finish, keep one unmachined witness face for the first-article report, because you cannot measure a coated pocket accurately without it.

• 1
  Threads after coatingHardcoat can add 25–50 μm per side.
• 2
  Define chamfersPowder coating rounds sharp edges.

Ask for the machine list, not a brochure photo. Window and door work needs long-travel mills for mullions, a 4th axis or mill-turn for roller and lock bodies, and a 5-axis center for angled hardware pockets. A shop with only small 3-axis machines will split your part, and you will pay for that in fit-up on site.

Certification is a filter, not a score. ISO 9001:2015 covers process control, IATF 16949:2016 adds traceability discipline, and ISO 27001:2022 covers how your drawings are stored. For a facade package the last one matters more than buyers expect, because profile drawings and hardware schedules are commercially sensitive.

Quote format tells you how the shop thinks. A one-line price with no alloy temper, no stock form and no inspection note is a guess. A usable quote names the material grade, the stock size, the datum faces, the finish spec, the sampling plan and the report you will receive. It should also say what the shop will do if the first article fails.

• 1
  Machine fit4,000 mm travel for mullions, 5-axis for angled pockets.
• 2
  TraceabilityAsk for a first-article report and material certs.
• 3
  Quote qualityNo datum list means no real process plan.